Quartz monzonite and monzonite

Unit symbol: Klqm
Age range Late Cretaceous (86.3 to 72.1 Ma)
Lithology: Igneous - Plutonic
Group name: Intermediate granitic rocks
Massive, coarse-grained, light-gray porphyritic quartz monzonite (Detterman and Reed, 1980; Nelson and others, 1983) is associated spatially with the Alaska-Aleutian Range batholith in the Iliamna and Lake Clark quadrangles. K/Ar ages range from 85.5 to 75.6 Ma (Reed and Lanphere, 1972). In northern Tyonek quadrangle, fine- to medium-grained pink monzonite or syenite intrudes sedimentary rocks of unit Kfy and contains primary pyroxene and has yielded a concordant U/Pb zircon age of 80.3±0.1 Ma (P.J. Haeussler, USGS, unpub. data). Pluton is distinctive in being more potassium-feldspar-rich and quartz-poor than other granitic rocks in the region. Unit also includes undated plutons in the Talkeetna Mountains quadrangle. In the west-central Dillingham quadrangle an unusual highly potassic coarse-grained biotite-pyroxene granite or syenite yielded an 40Ar/39Ar age of 84.49 Ma; this pluton is similar to other potassium-rich rocks in the Dillingham area (see unit TKg) except for age

Source map information

Source map Detterman, R.L., and Reed, B.L., 1980, Stratigraphy, structure, and economic geology of the Iliamna quadrangle, Alaska: U.S. Geological Survey Bulletin 1368-B, 86 p., 1 sheet, scale 1:250,000.
Symbol Kqm
Unit name Quartz monzonite
Description Massive, coarse-grained light-gray porphyritic quartz monzonite.
Lithology Igneous

Correlated geologic units

Label Kgk
Description Quartz monzonite, monzonite, and syenite [< 85 Ma]
Geologic age Santonian to Campanian
Geologic setting Intrusive
Lithology Form Importance
Monzonite < Syenitic < Plutonic < Igneous Pluton Indeterminate, major
Quartz-monzonite < Syenitic < Plutonic < Igneous Pluton Indeterminate, major
Syenite < Syenitic < Plutonic < Igneous Pluton Indeterminate, major